An inorganic spheroidized particle is obtained by melting a raw material powder produced by crushing silica rock in high-temperature flame and spheroidizing this powder by its surface tension.
For example, highly-pure spheroidized silica that is obtained by using silica rock as a raw material is widely used as a filler for an epoxy-sealing material of a semiconductor device, and a lot of merits such as improved fluidity of a sealing material, high filling amount, and improved abrasion resistance can be obtained by spheroidizing.
In the present description, an inorganic spheroidized particle may be simply described as a spheroidized particle.
As a prior art regarding the production of an inorganic spheroidized particle, there are the methods disclosed in Patent Literatures 1 to 4.
Because high-temperature flame is needed for the spheroidizing of raw material powder, a burner of an oxygen-gas combustion system is usually used.
Examples of the burner include a premixing type burner and a diffusion type burner. In a premixing type burner, oxygen and a fuel gas are preliminarily mixed and ejected to the combustion place. Meanwhile, in a diffusion type burner, oxygen and a fuel gas are separately ejected and mixed at the combustion place.
The premixing type burner is used in the method disclosed in Patent Literature 2, while the diffusion type burner is used in the methods disclosed in Patent Literatures 1, 3 and 4.
The diffusion type burner disclosed in Patent Literature 1 has the concentric double pipe in which a lot of small pipes are provided between the inner pipe and the outer pipe. This burner is disposed in a vertical furnace, a silicon raw material is flowed down spontaneously or flowed down with pressurization through the central pipe (inner pipe) of the burner, and the raw material powder is supplied into flame made by a fuel gas from the small pipes and an oxygen gas from the outer pipe to thereby produce a melted silica spheroidized body.
In the premixing type burner disclosed in Patent Literature 2, raw material powder, oxygen, and LPG are sufficiently mixed in a burner, and the raw material powder is supplied into flame made at the end of the burner.
The diffusion type burners disclosed in Patent Literatures 3 and 4 have the concentric quartet pipe structure in which a raw material powder is supplied into the combustion chamber from the center using oxygen or an oxygen-enriched air as a carrier gas, a fuel gas is supplied through the outer circumference thereof, the primary oxygen and the secondary oxygen are supplied through the further outer circumference thereof, and cooling water path is provided around the most outer circumference to thereby cool a burner.
In addition, Patent Literatures 3 and 4 disclose an apparatus that uses such a diffusion type burner to produce inorganic spheroidized particles.
In the production apparatus of inorganic spheroidized particles disclosed in Patent Literature 4, as shown in FIG. 6, a raw material powder is cut off from a raw material feeder A and carried to a burner B, together with a carrier gas that is supplied through a carrier gas supply device A′. Into the burner B, oxygen from an oxygen supply equipment C and a liquefied petroleum gas (LPG) from a LPG supply equipment D are supplied.
An exhaust gas containing particles spheroidized in flame in a vertical furnace E are cooled with air introduced into the bottom portion of the vertical furnace E through a path F, and then the spheroidized particles are collected by the following cyclone G and bag filter H.